12. A motorcycle officer hidden at an intersection observes a car that runs thro

Question

12. A motorcycle officer hidden at an intersection observes a car that runs through a stop sign and continues at a
constant speed. The officer takes off 2.0 s after the car has passed by. She accelerates at 4.8 m/s2 until her speed is
30.0 m/s (about 65 mph), and then continues at that speed until she catches the car. She catches the car 1.80 km
from the intersection.
(i) What is the time for the officer to get to her full speed?
(ii) If the officer, once at full speed, takes an addition 56.875 s to reach the car then what is the total time since the
car passed the stop sign?
(iii) What is the speed of the car?

Explanation / Answer

i)

the acceleration = 4.8 m/s^2

final speed = 30 m/s^2

time = 30/4.8 = 6.25 s

ii)

the total time = 6.25+56.875+2 = 65.125 s

iii)

the speed of the car = distance/time = 1.8/65.125 = 27.63 m/s

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